This invention pertains to control of the flow of solids onto or off an inclined conveyor belt solids separator wherein lower movement of rolling solids is controlled by a combination scraper and gas jet control arrangement. The separating system is for separating spherically-shaped rolling solids from irregularly-shaped nonrolling solids and is especially useful for oil shale retorting processes using spherically-shaped solid heat carriers which are recycled through the retorting process.
It is sometimes necessary to separate spherically-shaped rolling solids from irregularly-shaped nonrolling solids. This invention relates to an appropriately inclined conveyor belt system for carrying out such separation when a dry, high temperature, compact, high capacity, confined system with controlled atmospheric emissions and with a high degree of adaptability to varying mass flow rates and solids mixtures is required. For example, the retorting of oil shale with spherical solid heat carriers requires that the heat carriers be separated in this manner from spent shale solids. The separation efficiency must be good while carry-over, loss or attrition of the spherically-shaped solids, e.g., heat carriers, is low. It is also desirable that the separating system be relatively compact and have relatively few moving parts in light of the mass of solids to be separated per unit time. It is difficult to achieve these requirements and at the same time maintain the desired separating efficiency of the system.
Copending applications Ser. No. 749,505, filed Dec. 10, 1976, entitled "Separation and Recovery of Heat Carriers in an Oil Shale Retorting Process", and Ser. No. 749,588, filed Dec. 10, 1976, entitled "Inclined Conveyor Belt Solids Separating System with Responsive Gas Control", which are owned by a common assignee and are incorporated herein, cover embodiments of a continuously restored inclined conveyor belt type separating system.
Application Ser. No. 749,587 describes an inclined conveyor belt separating system having upper and lower diagonally placed scraper blades. The upper side of the slanted lower scraper blade acts as downward boundary to movement of spherically-shaped rolling solids and as a divider between distinct separating sections of the belt. More importantly, the lower scraper acts as a control for obtaining the desired separating efficiency level of a separating system operated at reasonably high mass flow rates. The lower scraper deflects the downward moving spherically-shaped solids in a sideways, downward direction off a side of the conveyor belt. This prevents rapid channeling of the rolling solids off the belt and holds a proper amount of rolling solids on the belt. This lower control works in conjunction with the upper control and other feed controls to provide the desired degree of separating efficiency for a minimum length of belt and allows the belt to be divided into the maximum number of distinct separating sections. In a properly tuned or controlled system, the separating efficiency becomes dependent on length and reaches a maximum efficiency at a given length. Below this length, the separating efficiency decreases. Above this length, the separating efficiency is relatively constant. As a result, increasing the length does not increase separating efficiency. Moreover, in a properly controlled, maximum efficiency conveyor belt system, the rate of rolling solids passing through the lower control equals the rate of rolling solids fed onto the belt. Consequently, increasing the length of a belt does not increase the capacity of the system. As a result, there is little to be gained by using a conveyor belt system that is longer than the required length and a number of operating disadvantages arise. The capacity of the conveyor belt system may be greatly increased by dividing the length of the belt into distinct separating sections of the required minimum length, and by increasing the width of the belt. The lower control, that is, the control for the rolling solids, is the most important for obtaining and maintaining the desired maximum separating efficiency for a minimum of belt length. As the width of the belt is increased, the diagonal lower scraper blade control has a problem in moving the spherically-shaped rolling solids sideways and downward off the belt at a rate which is high enough or reactive enough to obtain and maintain the separating efficiency of the minimum required length of the belt. If the rate of removal is increased, channeling of the rolling solids is likely to occur. If the rate of removal is too low, flooding or over saturation of the minimum length of the belt occurs. When operating conditions fluctuate, a wide lower scraper control has difficulty in reacting fast enough to the changed conditions without causing some channeling of the rolling solids which would decrease separating efficiency.
Application Ser. No. 749,588 describes an inclined conveyor belt system with longitudinally directed jets of gas acting as the lower control system. This system has some advantages, but it is not suited to a minimum length, wide separating section, nor is it suited to dividing a belt into multiple separating sections of minimum length each.
In this invention, there is provided a lower control arrangement for an inclined conveyor belt which coactively combines a diagonally located scraper blade, a jet of gas directed diagonally and laterally along the upper side of the scraper blade, jets of gas directed longitudinally ahead or up stream of the scraper blade and diagonally directed jet of gas to increase the capacity of the conveyor belt separating system while maintaining the desired separation efficiency.